andrel wrote:
> On 30-3-2010 18:11, Darren New wrote:
>> andrel wrote:
>>>> How about the fact that the stars of the universe are all 
>>>> red-shifted the farther they get from *us*?  Or the fact that we 
>>>> seem to be the only creatures in the entire *universe* that 
>>>> broadcast radio signals?
>>>
>>> For the latter see the Drake equation.
>>
>> I'm familiar with it. What about it?
> 
> All we know that there are no radio signals broadcasted from a place 
> exactly the right time ago to be just reaching us now, send towards us, 
> and in a format that we recognize. Which is quite a long way away from a 
> conclusion that no signals are send at all.

Yes. Hence the "seems to". Anyway, you understand my point even if you 
disagree. :-)

>> Yep. That doesn't mean things are moving away from us. We can't 
>> measure whether they're moving away from us. All we can measure is the 
>> red shift. The assumption is that the red shift is caused by relative 
>> motion, and not the geometry of the universe.
> 
> I don't understand that last sentence, but that may be my physics 
> background.


We assume that the distant galaxies are red-shifted *because* they are 
moving away from us. We don't assume that the Milky Way has the lowest speed 
of light in the universe, or that time runs slower the farther you get from 
humanity, or that the gravitational constant is slowly increasing the 
farther you get from humanity.  *If* you assume that all other places in the 
universe will see the same thing when they look around, *then* all the 
galaxies must be moving away from each other.  *If* you assume we're in a 
unique and privileged place in the universe, there are all kinds of things 
that could be causing it.


-- 
Darren New, San Diego CA, USA (PST)
   Yes, we're traveling together,
   but to different destinations.

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On 30-3-2010 20:15, Darren New wrote:
> andrel wrote:
>> On 30-3-2010 18:11, Darren New wrote:
>>> andrel wrote:
>>>>> How about the fact that the stars of the universe are all 
>>>>> red-shifted the farther they get from *us*?  Or the fact that we 
>>>>> seem to be the only creatures in the entire *universe* that 
>>>>> broadcast radio signals?
>>>>
>>>> For the latter see the Drake equation.
>>>
>>> I'm familiar with it. What about it?
>>
>> All we know that there are no radio signals broadcasted from a place 
>> exactly the right time ago to be just reaching us now, send towards 
>> us, and in a format that we recognize. Which is quite a long way away 
>> from a conclusion that no signals are send at all.
> 
> Yes. Hence the "seems to". Anyway, you understand my point even if you 
> disagree. :-)

yes

>>> Yep. That doesn't mean things are moving away from us. We can't 
>>> measure whether they're moving away from us. All we can measure is 
>>> the red shift. The assumption is that the red shift is caused by 
>>> relative motion, and not the geometry of the universe.
>>
>> I don't understand that last sentence, but that may be my physics 
>> background.
> 
> 
> We assume that the distant galaxies are red-shifted *because* they are 
> moving away from us. We don't assume that the Milky Way has the lowest 
> speed of light in the universe, or that time runs slower the farther you 
> get from humanity, or that the gravitational constant is slowly 
> increasing the farther you get from humanity.  *If* you assume that all 
> other places in the universe will see the same thing when they look 
> around, *then* all the galaxies must be moving away from each other.  
> *If* you assume we're in a unique and privileged place in the universe, 
> there are all kinds of things that could be causing it.

hence my "We say that because we believe in Lorentz invariance" as a 
abbreviation of a couple of paragraphs like the one above ;)

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andrel wrote:
> hence my "We say that because we believe in Lorentz invariance" as a 
> abbreviation of a couple of paragraphs like the one above ;)

Lorentz invariance would explain it if time was running slower or the speed 
of light was different farther away as well.

-- 
Darren New, San Diego CA, USA (PST)
   Yes, we're traveling together,
   but to different destinations.

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On 30-3-2010 20:29, Darren New wrote:
> andrel wrote:
>> hence my "We say that because we believe in Lorentz invariance" as a 
>> abbreviation of a couple of paragraphs like the one above ;)
> 
> Lorentz invariance would explain it if time was running slower or the 
> speed of light was different farther away as well.
> 

No, differential time- and lightspeeds are incompatible with lorentz 
invariance of physical laws, because they should be invariant under 
translation and uniform velocity changes.
In particular Maxwell's equations are lorentz invariant and they imply a 
*constant* velocity at which E and B fields propagate (generally known 
as c).

It might be possible to modify Maxwell's equations to allow timevarying 
lightspeed and find a new invariant that for times close to our own 
reduces to Lorentz invariance, but I have not heard of anybody doing 
that trick.

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On 3/28/2010 3:53 PM, Darren New wrote:
> Patrick Elliott wrote:
>> Still, its an interesting idea, and explains nicely why your desk will
>> never "jump" all into one corner of the room, for no reason.
>
> I think we already knew that. If you work out the probability that
> happens, it's exceedingly low.
>
Well, not really. The presumption is still that it *can* do so. However, 
if there is a limit on what things can do that, such that a desk doesn't 
simply have almost "no" chance of doing such a thing, but *absolutely no 
chance*, then you have a difference situation. That is the point. 
Standard QM insists its possible, just so insanely improbable that you 
will never see it happen. But, if QM gets even more greatly limited, or 
virtually switched off, for objects whose size and density exceeds some 
specific factor... That is a whole different ball game, since it means 
your QM is trapped, like air in a balloon, and no longer has the "range" 
needed to cause you desk to do such a thing.

-- 
void main () {
   If Schrödingers_cat is alive or version > 98 {
     if version = "Vista" {
       call slow_by_half();
       call DRM_everything();
     }
     call functional_code();
   }
   else
     call crash_windows();
}

<A HREF='http://www.daz3d.com/index.php?refid=16130551'>Get 3D Models, 
3D Content, and 3D Software at DAZ3D!</A>

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Patrick Elliott wrote:
> Well, not really. The presumption is still that it *can* do so. However, 
> if there is a limit on what things can do that, such that a desk doesn't 
> simply have almost "no" chance of doing such a thing, but *absolutely no 
> chance*, then you have a difference situation. That is the point. 

Well, sure, but I never heard of anyone postulating that.

> Standard QM insists its possible, just so insanely improbable that you 
> will never see it happen. But, if QM gets even more greatly limited, or 
> virtually switched off, for objects whose size and density exceeds some 
> specific factor... That is a whole different ball game, since it means 
> your QM is trapped, like air in a balloon, and no longer has the "range" 
> needed to cause you desk to do such a thing.

QM also has probabilities that cancel out, such that there's zero 
probability of something happening in a combination where either individual 
event could happen. E.g., electron 1 might go to location X[*]. Electron 2 
might go to location X. Electron 3 might go to location X. But there is zero 
probability that all three will go to location X. Also, the likelihood that 
a photon will go somewhere far away at anything other than very close to the 
speed of light is zero (and not just very low), because the probabilities 
actually cancel out. You don't need to postulate an upper size on QM 
locality to get impossible events. And when "improbable" is "1/10^500 that 
any particle in the universe will ever do that", then yeah, that's pretty 
much impossible too.



[*] "location" in spacetime, i.e., an "event".

-- 
Darren New, San Diego CA, USA (PST)
   Yes, we're traveling together,
   but to different destinations.

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andrel wrote:
> No, differential time- and lightspeeds are incompatible with lorentz 
> invariance of physical laws, because they should be invariant under 
> translation and uniform velocity changes.

I see what you mean. Yes, I agree. My bad.

-- 
Darren New, San Diego CA, USA (PST)
   Yes, we're traveling together,
   but to different destinations.

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andrel wrote:
> On 30-3-2010 0:30, Darren New wrote:
>> How about the fact that the stars of the universe are all red-shifted
>> the farther they get from *us*?  Or the fact that we seem to be the only
>> creatures in the entire *universe* that broadcast radio signals?
> 
> For the latter see the Drake equation.

Or: http://xkcd.com/718/

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andrel wrote:
> On 30-3-2010 18:11, Darren New wrote:
>> andrel wrote:
>>>> How about the fact that the stars of the universe are all red-shifted
>>>> the farther they get from *us*?  Or the fact that we seem to be the
>>>> only creatures in the entire *universe* that broadcast radio signals?
>>>
>>> For the latter see the Drake equation.
>> 
>> I'm familiar with it. What about it?
> 
> All we know that there are no radio signals broadcasted from a place
> exactly the right time ago to be just reaching us now, send towards us,
> and in a format that we recognize. Which is quite a long way away from a
> conclusion that no signals are send at all.

I keep wondering... Is humanity *constantly* broadcasting radio signals in a 
simple format to nearby solar systems? What if aliens have a program exactly 
like SETI@Home, trying to find intelligence in noise from received radio 
signals, but neither party is sending anything?

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On 31-3-2010 4:40, Nicolas Alvarez wrote:
> andrel wrote:
>> On 30-3-2010 18:11, Darren New wrote:
>>> andrel wrote:
>>>>> How about the fact that the stars of the universe are all red-shifted
>>>>> the farther they get from *us*?  Or the fact that we seem to be the
>>>>> only creatures in the entire *universe* that broadcast radio signals?
>>>> For the latter see the Drake equation.
>>> I'm familiar with it. What about it?
>> All we know that there are no radio signals broadcasted from a place
>> exactly the right time ago to be just reaching us now, send towards us,
>> and in a format that we recognize. Which is quite a long way away from a
>> conclusion that no signals are send at all.
> 
> I keep wondering... Is humanity *constantly* broadcasting radio signals in a 
> simple format to nearby solar systems? What if aliens have a program exactly 
> like SETI@Home, trying to find intelligence in noise from received radio 
> signals, but neither party is sending anything?

The major things we have been sending is FM (and AM) modulated radio and 
TV. This is effectively a big signal in a very small bandwidth. If you 
make a spectrum it will turn up as an unexpected peak above the 
background. If you then become interested and look closer you will see 
that the spectral contend is not compatible with a line originating from 
an exited atom or molecule. So, if these aliens are at the right time 
and place and have a SETI project running they will detect us in a 
couple of centuries when the signal reaches them.
If they are listening but expect a different modulation scheme they 
might just skip the lucille ball show as a strange artifact.

ATM AFAIK nobody is sending a deliberately simple encoded message. I 
think the jury is not out on the question if that would be a good idea 
at all.

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